The present invention relates to a paste ejection apparatus for ejecting slurry-like paste in which a viscous substance and a filler component are mixed, such as conductive paste.
As a method of joining electronic parts such as a semi-conductive chip to a print board or a lead frame, a resin adhesive is used much. As a kind of resin adhesive, conductive paste has been known, in which a conductive component such as metal powder is added in the resin thereby to apply conductivity to the joint. Since the conductive paste has a function of the adhesive, and also can cause the joint to conduct electrically, it is much used in order to secure a semi-conductive element onto the board and cause the semi-conductive element to conduct to an electrode of the board.
This conductive paste is obtained by mixing a main component as a resin adhesive such as epoxy resin, curing agent for curing the epoxy resin, or cure accelerator, with metal powder having conductivity. As the metal powder, silver powder is much used. The conductive paste is supplied in the shape of slurry in which silver powder having each kind of shape in order to improve the conductivity, for example, a grain-shaped silver powder or flake-shaped silver powder, is mixed with the resin adhesive.
For an applying apparatus of applying this conductive paste, an ejection apparatus for ejecting the conductive paste is provided. A plunger type ejection apparatus has been known, which sucks the conductive paste into a cylinder room and ejects it by a reciprocating movement of a plunger. Since the ejection by the reciprocating of the plunger is performed only intermittently, in case that it is necessary to perform paste applying of high efficiency by performing the ejection incessantly, a multi-plunger type paste apparatus having plural plungers is generally used, for example disclosed in JP-U-02-078773 (Japanese Utility Model Application Publication Number: Hei02-078773).
For such the multi-plunger type paste ejection apparatus, it is necessary to eject the paste ejected from the respective plungers in order from one fixed ejection port. Therefore, its ejection apparatus has aport switching function. Regarding this port switching, generally, an opening surface of a cylinder block for which a plunger hole is provided is brought into slide-contact with a fixed block for which an ejection port is provided, and the opening portion of each plunger is communicated with the ejection port in order. In this type, the slide-contacting surface between the opening surface of the cylinder block and the fixed block function as a seal portion for preventing the paste from leaking between the two members. Therefore, such paste leakage preventing measures are adopted that surface-finishing of high accuracy for this slide-contact surface in parts working in order to prevent occurrence of clearance, and use of a mechanism which applies the predetermined surface pressure at the operation time.
However, since the conductive paste is the slurry including a large amount of filler components such as silver powder and solid particles, in the conventional paste ejection apparatus, depending on constituent parts, the solid particles interposed between the slide clearance of the seal portion are easy to be attached onto the sliding surface, so that closeness of the sliding surface is hindered and it is not prevented that the paste leaks from the seal portion to the outside.
In addition, in such the paste ejection apparatus, the slurry-like liquid that is high in viscous and includes the metal powder is ejected. Therefore, since leakage of the liquid inside the ejection mechanism causes a bad operation and parts wear, the plunger sliding portion and the port switching portion require high sealing ability. However, generally to secure the high sealing ability increases sliding resistance of the plunger. Therefore, a load onto the drive mechanism which reciprocates the plunger increases, so that a large-sized drive mechanism is required. As described above, it was difficult to realize a compact paste ejection apparatus which secures the high sealing ability.
Therefore, an object of the invention is to provide a paste ejection apparatus which can prevent the paste from excessively leaking from the seal portion.
Furthermore, another object of the invention is to provide a small-sized and compact paste ejection apparatus which can secure the high sealing ability.
In accordance with the invention, there is provided a paste ejection apparatus for ejecting slurry-like paste in which a viscous substance and a filler component are mixed, comprising: a cylinder block being rotatable about a rotational axis by a rotation drive means, and contacting slidably with a seal surface of a seal member through a slide surface orthogonal to the rotational axis; plural cylinder holes provided in the direction of the rotational axis of the cylinder block and including opening portions formed at equal intervals on the same circumference of a circle having the rotational axis of the slide surface as a center; a plunger inserted into each cylinder hole; a plunger drive means reciprocating this plunger in synchronization with the rotation of said cylinder block; first and second communicating ports provided on the seal surface and communicating with the opening portions of the cylinder holes in the predetermined rotary position of the cylinder block; first and second external ports communicating respectively with the first and second communicating ports through the seal member; a housing portion located on the peripheral side of the seal surface, closed and surrounded by the seal member and the cylinder block to be a circular ring-shaped space; and a ring-shaped external seal member attached into the housing portion, including a first seal material having self-lubrication and a second seal material being rich in elasticity.
Furthermore, in the paste ejection apparatus according to the invention, the housing portion is formed by opposing an outer surface of the seal member to an inner surface extending axially from the cylinder block.
Furthermore, in the paste ejection apparatus according to the invention, the second seal material of the external seal member is fitted onto the outer surface of the seal member, and the first seal member of the external seal member slidably contacts with the inner surface of the cylinder block.
In another aspect of the invention, the housing portion is formed by opposing an inner surface extending axially from the seal member to an outer surface of cylinder block.
Furthermore, in the paste ejection apparatus according to the invention of the above aspect, the first seal member of the external seal member slidably contacts with the outer surface of the cylinder block, and the second seal material of the external seal member is fitted onto the inner surface of the seal member.
Preferably, the first seal member has a recess portion, and the second seal member is held by the recess portion of the first seal member.
In another aspect of the invention, the paste ejection apparatus comprises cylinder block being rotatable about a rotational axis by a rotation drive means, and contacting slidably with a seal surface of a seal member through a slide surface orthogonal to the rotational axis; plural cylinder holes provided in the direction of the rotational axis of the cylinder block and including opening portions formed at equal intervals on the same circumference of a circle having the rotational axis of the slide surface as a center; a plunger inserted into each cylinder hole; a plunger drive means reciprocating this plunger in synchronization with the rotation of said cylinder block; first and second communicating ports provided on the seal surface and communicating with the opening portions of the cylinder holes in the predetermined rotary position of the cylinder block; first and second external ports communicating respectively with the first and second communicating ports through the seal member; a housing portion located on the peripheral side of the seal surface, closed and surrounded by the seal member and the cylinder block to be a circular ring-shaped space; a ring-shaped external seal member attached into this housing portion; and a run-out constraining means for constraining run-out displacement in the diameter direction of the cylinder block near the external seal portion slidably contacts with the cylinder block.
Preferably, the housing portion is formed by opposing an outer surface of the seal member to an inner surface extending axially from said cylinder block; the inner surface side of the external seal member is fitted onto the outer surface of the seal member; and the outer surface side of the external seal member slidably contacts with the inner surface of the cylinder block.
In another aspect of the invention, the paste ejection apparatus for ejecting slurry-like paste in which a viscous substance and a filler component are mixed, comprises: a cylinder block being rotatable about a rotational axis by a rotation drive means, and contacting slidably with a seal surface of a seal member through a slide surface orthogonal to the rotational axis; plural cylinder holes provided in the direction of the rotational axis of the cylinder block and including opening portions formed at equal intervals on the same circumference of a circle having the rotational axis of the slide surface as a center; a plunger inserted into each cylinder hole; a plunger drive means reciprocating this plunger in synchronization with the rotation of said cylinder block; first and second communicating ports provided on the seal surface and communicating with the opening portions of the cylinder holes in the predetermined rotary position of the cylinder block; and first and second external ports communicating respectively with the first and second communicating ports through the seal member; furthermore the plunger drive means includes; a cam portion provided on the rotation drive means side of the cylinder block, and having cylindrical recess portions formed so that the drive end sides of the plural plungers can enter therein; a cam groove formed on the inner surface of said cylindrical recess portion and converting the relative rotating movement for the cam portion of said cylinder block into the reciprocating movement of the plunger in the direction of the rotational axis; and a cam follower coupled to the drive end side of each of the plural plungers, and rotating and moving into the cam groove thereby to transmit the reciprocating movement to the plunger.
Furthermore, the cam portion is constituted by combining two end cams each having a cam surface in the direction of the rotational axis in a state where the cam surfaces are opposed to each other.
According to the invention, on the peripheral side of the seal surface between the fixed seal member and the rotating cylinder block, the housing portion which is circular ring-shaped space closed and surrounded by the seal member and the cylinder block is provided, and the nearly ring-shaped external seal member comprising the self-lubricant material and the material that is rich in elasticity is attached into this housing portion, whereby it is possible to prevent the paste which has leaked from the seal surface from leaking to the outside of the housing by the external seal member.
Further, according to the invention, such the constitution is adopted that on the peripheral side of the seal surface between the fixed seal member and the rotating cylinder block, the housing portion which is circular ring-shaped space closed and surrounded by the seal member and the cylinder block is provided, the nearly ring-shaped external seal member is attached into this housing portion, and the run-out displacement is constrained in the diameter direction of this cylinder block near this external seal portion, whereby sealing ability when the paste that has leaked from the seal surface is prevented from leaking to the outside of the housing by the external seal member is improved, and wear of the external seal member can be reduced.
Further, according to the invention, as the plunger drive means for reciprocating the plural plungers, there are the cam portion which has therein cylindrical recess portions which the drive end sides of the plural plungers can enter; the cam groove for converting the rotating movement into the reciprocating displacement in the direction of the rotational axis, which is formed on the inner surface of the cylindrical recess portion; and the cam follower rotating and moving into this cam groove, which is coupled to the drive end side of the plunger, where by under the high sliding resistance condition, in either case of the going movement and the returning movement of the plunger, the drive power can be surely transmitted, high sealing ability is secured, and the dimension in the diameter direction can be reduced, so that a small and compact paste ejection apparatus is realized.